The costs to launch a rocket into Earth orbit can run into the millions of dollars. As a rocket can carry multiple satellites and other equipment, the cost of the launch can be allocated among the different payloads. Consequently, smaller satellites might incur smaller costs to get into orbit. The measure of a size of a satellite could relate to its mass, its volume, its height, width and depth, as well as its shape. As for shape, it might be that the cost of getting equipment onto a launch bay is a function of the envelope of the satellite.
In view of these considerations, nanosatellites are often deployed, especially where the desired functionality fits in a nanosatellite form factor and where a constellation of satellites are needed. The term “nanosatellite” often refers to an artificial satellite with a wet mass between 1 and 10 kg, but it should be understood that features might be present in satellites outside that range. A constellation of smaller satellites might be more useful than one large satellite for the same or similar construction and launch budget. However, the result is usually that a rocket payload comprises many more independent vehicles.
To accommodate a large number of independent satellites, rocket logistics often dictate that the satellites be rectangular prisms or other shapes that are space-filling. For example, some nanosatellites are generally cube shaped. Typically these satellites include propulsion, solar panels for on-board electrical power generation, and communications capabilities. Some satellites are used for imaging and might include a telescope assembly for light gathering and a camera assembly for converting gathered light into electronic data, which can then be processed on-board and/or communicated to another satellite or a ground station.
For a celestial imaging system that has missions to capture images of the Sun, the Moon, starts and other astronomical objects, the particular orbit might not matter. However, for Earth-observing satellites, closer is better. Of course, there are limits to how low an orbit can be and still be viable. As a result, such a satellite is performing as a terrestrial long distance imaging system, and has a number of challenges. One is the distance between the satellite and the target of an imaging process. Another is that the satellite is not anchored, so internal movements can cause rotations of the satellite. Also, the satellite is moving at a high speed in order to maintain its orbit, which means the satellite is not stationary with respect to the target. The terrestrial long distance imaging system has to also deal with the conditions of operating in space and the stress of launch.
For imaging purposes, a satellite might have to address significant size and operational constraints, such as the resolution of images and spectra covered. The light available to a satellite might be limited by the amount of time available for image capture. Consequently, there are a number of areas in which satellite imaging systems can benefit from improvement